Heaters are used in plastic molding operations to keep the molding material in a fluid state during molding operations. Unfortunately, such heaters can collect moisture from condensation and the like. A heater that has a sufficient amount of moisture can have dangerously high leakage currents as a result of this moisture that can damage or destroy the heater and related equipment and possibly cause injury if full heater power is applied when this moisture is present.
If too much moisture is present in the heater, then it is necessary to service and possibly repair the heater prior to its being used. However, if only a moderate amount of moisture is present in the heater it is possible to remove the moisture by drying and then put the heater into use. This drying can be accomplished by applying only a small amount of power to the heater until the heater is dried out. However, if this drying is accomplished with too much voltage then internal heater arcing can occur inside the magnesium oxide heater insulator which leaves carbon deposits inside the heater. Such carbon deposits inside the heater adversely affect heater performance and cause permanent heater deterioration.
It is of course possible to manually apply a comparatively low voltage to the heater to attempt to dry it out blindly, but this is in practice not efficient and does not avoid possible heater damage. Also, if a severe moisture problem is present or a ground fault occurs then the heater would potentially be damaged and should not be used, but instead should be shut down. A definite need exists to automatically check a heater for moisture and/or a ground fault situation and to shut down the system if necessary or to dry out the heater if it is possible and to dry it out in a manner that minimizes heater damage.
This invention overcomes these problems associated with the use of heaters that may have moisture that could cause damage to the heater and allows the heater to be checked for the presence of moisture or a ground fault. The invention shuts down the system if a dangerous situation exists or subjects the heater to dry out cycles to allow it to be operated normally if it is possible. This drying out of the heater is accomplished in such a manner that heater damage is minimized.